Demister pads

Coalescing demister pads have been used in some single absorption plants instead of packed fiber beds to remove mist from the stack gas. For submicrometer particle collection, these devices are not as efficient as packed fiber beds. Nevertheless, they have been used in some plants to obtain nearly... 

Can be fabricated from variety of materials. Inexpensive to operate. Gas and liquid contact in lower bed. Dry upper bed, mist eliminator, or demister pad. selected. 

Effective inlet air filtration is required to ensure satisfactory operation of the engine. The location of the unit determines the most appropriate filter system to use. Desert environments where a large amount of sand particles could be expected in the ambient air may use an automatic roll type of filter that allows new filter material to be rolled in front of the inlet without frequent shut-downs to change filters. Arctic or extremely cold locations may use pad type filters, snow hoods to prevent blockage, and exhaust recirculation to prevent icing. Filter assemblies for offshore marine environments may include weather louvers, demister pads, and barrier elements for salt and dirt removal. Screens may be u.sed for insect removal prior to filtration in areas with bug problems. 

The four stage exhaust box Includes the oil box separator, the demister pad, the oil mist eliminator, and the synthetic oil baffle. Additional features include ein automotive type spin-on oil filter, a built-in inlet anti-suckback valve that prevents oil from being drawn into the system when the pump is stopped, eind a built-in gas ballast, available on the RA version, which permits pumping with high water vapor loads. 

If a demister pad is not used, the value of u, obtained from equation 10.10 should be multiplied by a factor of 0.15 to provide a margin of safety and to allow for flow surges. 

As the separation of condensate from steam is unlikely to be critical, a demister pad will not be specified. 

Fog formation. In the condensation of a vapour from a non-condensable gas, if the bulk temperature of the gas falls below the dew point of the vapour, liquid can condense out directly as a mist or fog. This condition is undesirable, as liquid droplets may be carried out of the condenser. Fog formation in cooler-condensers is discussed by Colburn and Edison (1941) and Lo Pinto (1982). Steinmeyer (1972) gives criteria for the prediction of fog formation. Demisting pads can be used to separate entrained liquid droplets. 

Entrainment Separators. In any process in which the product is volatilized, including both Gas Recycle and Liquid Recycle, ppm or ppb levels of metal catalyst may be entrained in the vapors leaving the separation system. Entrainment separators (Figure 2.9) are often included to recover the metal. Vaporous product effluent from a gas recycle reactor may be sent to a separator where it is passed through a demisting pad to return some aldehyde and condensation product and particularly to prevent potential carryover of catalyst. [6]... 

TPU-116 liner, single pack (burner), an ultraviolet flame scanner, a TPU sump pump, a scrubber demister pad, inlet water filters, and an inlet recirculation valve (D17789D, p. 40). 

The amount of hardness deposits in steam is a function of entrainment of water, as well as the TDS of the boiler feedwater. A well-designed boiler, then, often is equipped with a mesh-type demister pad to remove entrainment from the produced steam. 

Figure 26.1 shows an 8-in-thick demister below the top head. A demister pad resembles a giant Brillo pad without the soap. Many process plants have discarded demister pads lying around their scrap heaps, so you may have already seen what they look like. 

The dislodged sections of the demister pad are blown into downstream equipment, as into the suction of a centrifugal wet-gas compressor. 

Regarding the need for absolute removal of all free liquid mist, such as with a gas turbine compressor suction scrubber, I find a 100-pm particle size selection to be good design practice. This particle size fallout before reaching a demister pad will indeed ensure that most any demister pad will remove all remaining free liquid mist. 

Caution I have known a few demister pad vendors to claim that their pads would remove even a 500-pm particle and yet sustain absolute mist-free discharge. I have serious reservations here. Why First, I have yet to witness myself, or even hear a truly unbiased witness testify, that this is true. Can a 500-pm selection be achieved for absolute mist removal in a demister pad Second, I leave this question to those... 

Gas-phase liquid particle. The gas-phase liquid particle size of choice is generally 150 pm or less, which results in excellent gas-phase separation of liquids. For more critical liquid particle removal, such as with turbine blade gas suction, a 100-pm particle size input is recommended with a supporting demister pad in the separator. 

The steam may be purified by Droplet Separation techniques such as knitted wire mesh demister pads, wave plate separators and fiber pad separators using PTFE fibers. It can also be purified by scrubbing devices such as packed columns, venturi scrubbers, and irrigated sieve plates. Sometimes a combination of Droplet Separators and Scrubbers are used because AN emissions from neutralizers are very difficult to remove due to the very fine particles103. 

For the 12.7 cm column, the gas and slurry distributor was 1.25 mm thick, with, a 1Q to 13 open area of 0.9 mm holes. The 30.5 cm column used different 0.3 open area, distributor plates, with 0.9, 3.2 and 12.7 mm diameter holes. The gas traveled with the slurry, separated at the column top, and passed through a demister pad, liquid trap, and rotameter before being vented. 

PTFE, known under the trade names Teflon and Fluon, is resistant to all chemicals, except molten alkalis and fluorine, and can be used at temperatures up to 250°C. It is a relatively weak material, but its mechanical strength can be improved by the addition of fillers (glass and carbon fibers). It is expensive and difficult to fabricate. PTFE is used extensively for gaskets, gland packings (for example, on valve stems), and demister pads. As a coating, it is used to confer nonstick properties to surfaces, such as filter plates. It can also be used as a liner for vessels. 

Impingement settlers 10.8.2 Demisting pads 10.9 (Absorption) Volume 2... 

Knitted mesh demisting pads are frequently used to improve the performance of separating vessels where the droplets are likely to be small, down to 1 pm, and where high separating efficiencies are required. Proprietary demister pads are available in a wide range of materials, metals and plastics thicknesses and pad densities. For liquid separators, stainless steel pads around 100 mm thick and with a nominal density of 150 kg/m would generally be used. Use of a demister pad allows a smaller vessel to be... 

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